Light emitting diode (LED) based illumination lighting has limitations. LEDs, for example, typically emit light over a rather broad angular output field, typically called Lambertian angular distribution with 120-degree beam angle (full-width at half-maximum). To achieve high brightness and a narrow beam, for example for use in a high bay light application, many LEDs are needed which increases the weight and bulkiness of the luminaire. Even with optical elements to somewhat narrow the output angle range, some light often is lost outside the desired area of illumination, for example, at ground or floor level in the high bay light application. Achieving a high brightness and a narrow beam in a downlight application also requires a luminaire with a large form factor.
Laser light sources are good pumping sources and have high power in a relatively small package with extremely strong directionality. But because of safety concerns and low optical efficiency, blue laser light sources are typically not utilized as a light source for illumination lighting in the lighting industry. Blue laser light is not dangerous because of the wavelength of blue colored light, but rather because the laser light beam is highly focused and coherent, resulting in a high power density light source.
Although blue laser light sources have been utilized in automobile headlamp applications, the designs for those lighting devices involve several mirrors to deflect the blue laser light and have many air gaps. The air gaps and mirrors in the design of such lighting devices are problematic for several reasons. In the event of breakage of the lighting device (e.g., during an automobile accident), the blue laser light is not confined and escapes outside, which can harm a living organism exposed to the blue laser light directly, or even indirectly. Accordingly, incorporating a blue laser light source into a lighting device for illumination lighting in a safe and optically efficient design is difficult.